Looking for a notes app that is supported on multiple platforms

I've been using MyScript notes for school for a while now, but I'm beginning to run into its limitations for the kind of stuff I do. I was wondering if anyone could provide a good recommendation for me. My criteria is as follows:

1. MUST support stylus notes in a straightforward and thorough way

2. good folder organization, the closer it is to letting me organize notes and books as if it were a file explorer, the better

3. must be able to create documents in different paper sizes and allow me to export them as pngs and pdfs.

My use case is primarily STEM, and beyond that, the only thing I would consider a nice-to-have feature would be an infinite whiteboard feature. I also would need it to be supported on Mac, Windows, and iPadOS.